1. Field of the Invention
This invention relates to a method for providing dynamic control of signal power levels in a bidirectional backhaul communication link between the base station and the repeater station in a wireless cellular communication system. More specifically, the invention relates to power controlling apparatus in both the base station and repeater station which uses suitable hardware and software to dynamically control the signal power levels between the base station and repeater.
2. Description of Related Art
In the field of wireless cellular communication, demand for services is constantly increasing. Typically, the operators of analog and digital cellular telephony services are required to upgrade the capacity of their systems within a given service area as customer demand grows. To meet the needs of an increased number of subscribers in a predefined service area, the service provider must modify the existing equipment to accommodate the increased traffic demands of a growing number of users.
A typical cellular phone system architecture includes a network of cells, mobile radio units, and a base transceiver station (BTS) located within each cell. The BTS is controlled by a central base station controller (BSC), and both are connected to a mobile telecommunications switching office (MTSO). The MTSO in turn routes calls to a standard public switched telephone network (PSTN) for land line communications. Increasing numbers of subscribers place a growing demand on the BTS to service an ever increasing number of calls in its respective cell. As a result of this increased demand on BTS capacity, BTS technology is constantly being improved and upgraded.
One way of alleviating increased BTS demand is described in U.S. Pat. No. 5,970,410 by Carney et al (Carney), entitled xe2x80x9cCellular System Plan Using In Band Translators to Enable Efficient Deployment of High Capacity Base Transceiver Systems.xe2x80x9d Instead of placing a base station in each cell, Carney describes a system with a home base station located in central cell serving one or more repeater stations located in substantially adjacent cells. Communication signals from mobile transceiver units located in the cells served by repeater stations are received by the repeater station and are then sent to the serving home base station via a backhaul communication link. The backhaul link is a bi-directional radio link between the serving base station and the associated repeaters, and provides the backbone communication link between the base station and the repeaters.
In a Carney-type repeater-based system, both the repeater stations and the base stations are initially deployed so that the backhaul link operates at a fixed, predetermined signal power level. However, if any conditions occur that might cause the backhaul signal strength of the received signal at the base station or repeater to vary, neither the base station nor the repeater can, without technician intervention, modify its transmitted signal strength to ensure that the signal is received at its required level.
Certain terrestrial conditions, such as fading caused by a water surface or attenuation due to changing atmospheric conditions, can cause the received signal power levels at the base station repeater to drop by as much as 30 dB. If the power level drops below a minimum threshold level, then the signal may be lost. Furthermore, if the backhaul channel signal is received by the repeater at a signal power level less than the minimum level control range (e.g., xe2x88x9295 dBm), then the level at which the signal is re-transmitted to the mobile station is transmitted at the same reduced signal power level. For example, if the backhaul signal power level received by the repeater is xe2x88x9298 dBm, then the signal is re-transmitted to the mobile station at +43 dBm, or 3 dB below the nominal specified transmission level of +46 dBm. In such cases where the backhaul signal is received by the repeater at levels below xe2x88x9295 dBm, the signal may be lost by the mobile receiver and the call dropped. This presents an intermittent maintenance problem to ensure proper operation of the system.
In addition, different distances between the home base station and the repeater stations require different transmit power levels to ensure that the received backhaul channel power levels are within a predetermined installation target level. This means that a qualified service technician must be available upon installation of the repeater to set the transmitter output power to a suitable level. Further, another technician is required at the base station receiving end to provide feedback to the remotely located technician regarding received signal strength. The time and expense involved in such installation procedure is undesirable.
Presently, in cellular systems, including repeaters, the only way to compensate for varying received backhaul signal power levels caused by terrestrial and atmospheric conditions is to manually adjust the transmit power levels at the repeater stations in the field. Similarly, manual setup adjustments need to be performed for transmitter signal power levels due to different distances between repeaters and base stations. Technicians are required to visit the repeater station site and to physically adjust the transmit power accordingly when received power levels are not within a predetermined target level. Manual field adjustment is an unsatisfactory solution because it requires time consuming, expensive maintenance and monitoring of repeater stations. Further, the transient nature of signal fading is problematic, requiring repeat visits to the site as the condition changes over time. In addition, repeaters must be located close enough to the base station to guarantee that received backhaul signal levels remain at a predetermined target level, despite transient variations caused by external conditions.
The invention concerns a wireless cellular communication system having a base station located within a home cell and at least one substantially adjacent cell. The adjacent cell has a repeater station located therein for facilitating communication between the base station and mobile units located in the adjacent cells. In one embodiment, the invention provides a method for dynamic control of signal power levels in a bi-directional backhaul communication link between the base station and the repeater station. In this embodiment, a received signal power level of a signal transmitted between the base station and the repeater station is measured in a receiving one of either the base station or the repeater station. Power level data is produced, based on the measured received signal power level and is then automatically transmitted to either the base station or repeater station which was the source of the signal. Finally, the source of the measured signal receives the power level data. The method can further include automatically adjusting the power level transmitted by the source of the measured signal when the power level data indicates that the received signal power level has deviated from a predetermined power level.
According to one embodiment, the power level data indicates the received signal power. Alternatively, the power level data may be a request directed to the source to control the transmitted power for increasing, decreasing, or maintaining the transmitted power.
The method can further include transmitting the power level data within a defined channel of the backhaul link assigned to at least one of the mobile units. According to one aspect of the invention, the backhaul link is a time division multiplex (TDM) type channel. Further, the invention can include a method for monitoring the backhaul communication link to identify an available TDM time slot and transmitting the power level data within the available time slot. According to one embodiment, the available time slot is a mobile unit control channel time slot. The method can further include suppressing the control channel data received from the mobile units in the control channel time slot when transmitting the power level data in the control channel time slot.
In another embodiment, the invention further provides an apparatus for dynamic control of signal power levels in a bi-directional backhaul communication link between the base station and the repeater station. This embodiment provides suitable signal processing circuitry and/or software to measure a received signal power level of a signal transmitted between the base station and the repeater signal power in a receiving one of either the base station or the repeater station. Modulating, transmitting, and associated control circuitry and/or software is also provided to automatically transmit power level data to the source of the measured signal. This power level data is produced based on the received signal power level from the receiving base station or repeater. In addition, receiving and associated control circuitry and/or software is provided in the source to receive the power level data. The invention can also include suitable control circuitry, or software, or a combination thereof, to automatically adjust the power level transmitted by the source of the measured signal when the power level data indicates that the received signal power level has deviated from a predetermined power level.
According to one embodiment, the power level data can be the received signal power level. In an alternative embodiment, appropriate circuitry and/or software can be provided so that the power level data may be encoded as a request directed to the source to control the transmitted power for increasing, decreasing, or maintaining the transmitted power.
The invention can further include modulating, transmitting and associated control circuitry and/or software to transmit the power level data within a defined channel of the backhaul link assigned to at least one of the mobile units. The power level data can then be transmitted using appropriate modulating, transmitting and associated control circuitry and/or software together with either the control or traffic data within the defined channel of the backhaul link which is assigned to the mobile unit.
According to another aspect of the invention, the backhaul link is a time division multiplex (TDM) type channel. Further, suitable signal processing circuitry and/or software can be provided for monitoring the backhaul communication link. This circuitry and/or software can identify an available TDM time slot and can transmit the power level data within the available time slot. According to one embodiment, the available time slot is a mobile unit control channel time slot. In that case, suitable signal processing circuitry and/or software can be provided to suppress the control channel data received from the mobile units in the control channel time slot when transmitting the power level data therein.